P097 | ROUTINE MULTIPARAMETRIC FLOW CYTOMETRY ANALYSIS QUICKLY RULE OUT HEMATOLOGICAL DISEASES IN CASE OF BONE MARROW NEOPLASTIC INVASION.

Background: Multiparametric flow cytometry (MFC) is a widely employed technique by hematologists for the characterization of cellular populations in peripheral blood, bone marrow (BM) or body cavity fluids samples, particularly in the context of hematological malignancies (HMs). Conversely, its application has been limited in detecting non-hematological neoplasms (non-HNs) due to the scarce specificity in identifying neoplastic cells of solid tumors. Nevertheless, MFC may aid in distinguishing cells of non-hemopoietic origin in patients with clinical suspicion of hematological disease and BM invasion with inconclusive cytomorphological findings. Patients e Methods: We retrospectively evaluated 8 cases of patients (median age 61.5 years; range 31-81) referred for suspected hematological disease to both Sapienza University and Sant’Eugenio Hospital Hematology Units (Rome), between October 2012 and March 2024. Patients underwent BM aspirate for cytomorphological examination and then BM samples were analyzed by 6-8-12 colors MFC (BD FACSCanto/FACSLyric^TM flow cytometers; BD Paint-A-Gate/FACSDiva^TM software), using combinations of in vitro diagnostic monoclonal antibodies (CD45/MPO/cCD3/CD79a/HLADR/CD34/CD117/CD13/CD33/CD41a/CD61/CD19/CD20/CD22/CD38/CD200/cVS38/CD138/Igκ/Igλ/TCRαβ/TCRγδ/CD2/CD5/CD7/CD4/CD8/CD28/CD16/CD11b/CD56). Results: Despite the evidence of BM infiltration, cell morphology was inconclusive in all cases. MFC revealed a median BM pathological infiltration of 43.1% (range 15-70%) of medium/large size elements (high SSC/FSC) which were positive for at least one antigen among CD56 (7 pts; 86%), CD117 (6 pts; 75%) and CD138 (6 pts; 75%), but all negative for CD45 (leukocyte common antigen), CD38 end all other lineage-specific antigens for T-cells, B-cells and myeloid cells. In two patients (25%) there was also a week expression of NG2, associated to CD146, CD200 and cVS38 in one case. Subsequent histological BM evaluation (5 pts; 63%) or specific tissue (3 pts; 37%) biopsies revealed infiltration by solid tumor cells. Conclusions: The CD45-/CD38-/CD56+/CD117+/CD138+/CD146+/CD200+/cVS38+/NG2+ pattern is not found in normal BM or in BM infiltrated by HMs but is highly suggestive for non-HNs. Even if flow cytometry is stereotyped in solid cancers, since the same pattern could be found whatever is the histological type, it is useful for quickly rule out HMs in patients with clinical suspicion of hematologic disease and inconclusive cells morphology.